LDPE (low density polyethylene) exhibits excellent blown film processability but relatively low stiffness and impact toughness. LDPE was made using peroxide initiated radical polymerization of ethylene and contains both short and long chain branches. The excellent processability of LDPE is believed to be due to the presence of long-chain branch structures (dense comb, tree-like, and dendritic structures), although such structures have not been characterized analytically.
HDPE (high density polyethylene) has purely linear PE chains without any long and short chain branches. HDPE exhibits excellent stiffness but poor mechanical toughness and blown film processability.
LLDPE (linear low density polyethylene) contains only short chain branches introduced through the addition of a linear alpha-olefin co-monomer. LLDPE has a heterogeneous composition distribution and exhibits good toughness and moderate stiffness but relatively low blown film processability.
mLLDPE (metallocene catalyst polymerized linear low density polyethylene) has a homogeneous composition distribution containing only short chain branches. mLLDPE exhibits excellent impact toughness and moderate stiffness but very poor blown film processability.
It would be desirable to have an additive for ethylene polymers and for propylene polymers that would enhance extensional hardness, processability, shear thinning, and melt strength. It would also be desirable to have an additive that does not significantly diminish impact toughness and mechanical stiffness of ethylene and propylene polymers.
Polyolefins with a comb-like topology or configuration can provide enhancement of physical properties of ethylene and propylene polymers. However, synthetic methods for comb polyolefins employed in the prior art have proven challenging to carry out, particularly when a tailored structure is desired. It would be desirable to have an effective and efficient process for making comb polyolefins, particularly those with tailored structures.
Polyolefins with a dense comb topology could be used as viscosity modifiers in lubricants. In addition to thickening the lubricant base stock, raising the viscosity index, delivering shear thinning, the comb-like polyolefins could potentially lower the contact friction of lubricants as comb structures are preferred in lubrication applications. It would be desirable to have a comb-like polyolefin that lowered the contact friction of lubricants.
Conventional polypropylenes exhibit only limited melt strength, which has resulted in processing difficulties in blow-molding of bottles and other articles. It would be desirable to have a polyolefin additive that would enhance the melt strength of conventional polypropylenes.